Discharge tube containing mercury

ABSTRACT

The invention relates to a discharge tube in which mercury is present in the discharge space and in which the lead-through conductor to an electrode of this lamp consists of copper-clad wire. According to the invention, the copper-clad wire is electrically oxidised. As a result, a lamp is produced whose lead-through conductor is substantially not attacked by mercury.

United States Patent [191 Willems DISCHARGE TUBE CONTAINING MERCURYHenricus Gerardus Antonius [75] Inventor:

Willems, Terneuzen, Netherlands [73] Assignee: U.S. Philips Corporation,New

' York, NY.

22 Filed: Aug. 20, 1973 [21] Appl. No.: 390,167

[30] Foreign Application Priority Data Sept. 12, 1972 Netherlands7212337 [52] US. Cl. 313/218; 313/210; 313/227 [51] Int. Cl. H01j 61/06[58] Field of Search 313/218 [56] References Cited UNITED STATES PATENTS2,065,947 12/1936 Nauth ..313/2l8 July 22, 1975 Primary Examiner-R. V.Rolinec Assistant Examiner-Darwin R. Hostetter Attorney, Agent, orFirmFrank R. Trifari; Robert S. Smith [57] ABSTRACT attacked by mercury.

3 Claims, 2 Drawing Figures DISCHARGE TUBE CONTAINING MERCURY Theinvention relates to a discharge tube having a wall of glass, which tubecontains at least mercury and is furthermore provided with an internalelectrode which is connected to an electrical lead-through conductormainly consisting of copper-clad wire, the part of said electricallead-through conductor located between the electrode and the glass wallbeing provided with an oxide coating, which coating is in direct contactwith the discharge space of the discharge tube.

Glow discharge tubes of the above-mentioned kind have been manufactured.In these tubes the oxide coating consisted of chromium oxide. Thiscoating served to prevent attack of the copper-clad wire by the mercurypresent in the discharge tube. A drawback of the aforementioned glowdischarge tube was its timeconsuming manufacture due to the extraprovision of chromium oxide.

In a further known discharge, lamp, namely a lowpressure mercury vapourarc discharge lamp, an electrical lead-through consisting of twodifferent wire pieces has been used in which the connexion, for example,a welded connexion, of these two wire pieces was located in the wall ofthe discharge tube and in which the wire piece remote from the dischargespace was copper-clad wire and the other piece consisted, for example,of nickel or another mercury-resistant material.

A drawback thereof was that the manufacture of the electricallead-through conductor was complicated and this because use had to bemade of these two wire pieces of different material and becausefurthermore a welded joint had to be provided between these wire pieces.

It is an object of the invention to manufacture in a simple manner adischarge tube of the kind described in the preamble, and to make thistube in such a manner that mercury substantially does not attack theleadthrough conductor in the completed tube.

According to the invention, a discharge tube having a wall of glass,which tube contains at least mercury and is furthermore provided with aninternal electrode which is connected to an electrical lead-throughconductor consisting mainly of copper-clad wire, and in which at leastthe part of said electrical lead-through conductor located between theelectrode and the glass wall is provided with an oxide coating, whichcoating is in direct contact with the discharge space of the dischargetube is characterized in that the said part of the lead-throughconductor consists of a copper-clad wire which is surrounded by a Cu Ocoating, the leadthrough conductor being manufactured in known mannerfrom a copper-clad wire of which part of the copper is oxidised duringheating by electrical process.

An advantage of a discharge tube according to the invention is that nooxide coating of a metal other than copper such as, for example, achromium oxide coating, need be provided on the copper-clad wire. Infact, when electrically oxidising copper-clad wire in known manner, asatisfactory oxide skin is produced such that it is also resistant tomercury present in the discharge tube.

The device consists in principle of a supply reel containing metal wireto be treated. The metal wire is guided into a cylindrical tube over acontact roller. This tube may be, for example, a glass tube which isprovided with a rubber stopper having an aperture through which the wirecan be guided into the tube with an ample amount of play, a side tubefor introducing gas, and a constriction. The wire is then guided into areservoir containing water round a contact roller and is then reeled onthe supply reel.

Copper core wire may be provided with a Cu O layer by means of saiddevice: copper core wire built up from a core, diameter 400 microns,consisting of a nickeliron alloy having nickel content of 42 percent byweight and a copper sheeth, thickness 50 microns, is guided through thetube at a rate of metres per minute. A gas mixture consisting ofnitrogen with 4 percent by volume of oxygen is introduced into the tubethrough a side tube at a rate of approximately 3 litres per minute. Thewire is heated by the direct passage of current at a temperature of950C. For that purpose, a voltage difference of approximately 40 V isset up between the contact rollers. The wire is loaded with 1.5 kW. Thecontact roller with which the wire is last in contact during thepassage, is arranged in running water so that a very rapid cooling fromthe oxidation temperature is obtained.

In this manner an even Cu O layer is formed, thickness approximately 1micron. This layer is red-coloured and CuO can not be demonstrated init.

A further advantage of a tube according to the invention is that awelded joint is absent in the lead-through conductor at the area of thewall of the discharge tube.

The discharge tube may be, for example, a low pressure mercury vapourdischarge lamp in which the discharge is an arc discharge.

In a preferred embodiment of a discharge tube according to theinvention, the tube is a glow discharge lamp.

An advantage of this preferred solution is that also in these generallyvery small lamps extra materials such as chromium oxide or extra weldedjoints in the wall are not required.

In a further preferred embodiment of a tube according to the invention,the connexion between the electrode and the lead-through conductor is awelded joint established electrically.

An advantage of this preferred embodiment is that also the welded jointis satisfactorily mercury-resistant. This would be the case to a muchlesser extent when a welded joint had been made in which the heattreatment would have been effected through gas flames, namely becausethe oxide skin of the copper-clad wire would have been attacked to astronger extent.

The invention will further be described with reference to a drawing.

FIG. 1 shows a glow discharge lamp according to the invention;

FIG. 2 shows an end part of a low-pressure mercury vapour discharge lampaccording to the invention, which lamp has an arc discharge in theoperating condition.

In FIG. 1, 1 is a glass envelope of a discharge space 2. This spaceaccommodates two electrodes 3 and 4. These electrodes are made of amercury-resistant electrode material, for example, molybdenum. Theelectrodes 3 and 4 are cylindrical. 5 and 6 denote two supply wires ofcopper-clad wire having a core of an iron alloy. These supply wires areelectrically oxidised. They pass through the glass wall 1. The supplywire 5 is connected to electrode 3 and supply wire 6 is connected toelectrode 4. The connexions between the supply wires and the electrodesare obtained by means of an electrical welding process. The dischargespace contains a rare gas, for example, neon or a combination of neonand argon, towhich mercury has been added. A luminescent coating, forexample, of willemite was present on the inner wall of the glassenvelope (1).

Experiments have proved that these lamps did not exhibitany attack ofthe copper-clad wire by the mercury, even after storage for one year. Ina gas-oxidised copper-clad wire an attack of the copper-clad wire wasalready found after two weeks.

In FIG. .2, 20 denotes an end part of a low-pressure mercury vapour arcdischarge lamp which is provided notes a pinch and 23 is a closedexhaust tube. 24 denotes a metal ring having connections pins 25 and 26arranged insulated therefrom. One end of an electrode 27 is connectedthrough an electrically oxidised copper-clad wire 28 to the connexionpin 25. The other end of the electrode 27 is connected through anelectrically oxidised copper-clad wire 29 to the connexion pin 26. Thesecopper-clad wires 28 and 29 pass through the glass wall of the dischargetube at the area of the pinch 22. Thus, 28 and 29 are the electricallead-through conductors.-

Likewise as in the lamp of FIG. 1, the copper-clad wires inthe case ofthe lamp part of FIG. 2 are also resistant to mercury present in thedischarge tube.

. electrical lead-through conductor located between the Also in the caseof the lamp part shown in FIG. 2, the connexions between the copper-cladwires 28 and 29 and the electrode 27 are obtained by an electricalweldelectrode and the glass wall is provided with an oxide coating, saidcoating being in direct contact with the discharge space of thedischarge tube, wherein said part of the lead-through conductor consistsof a copper-clad wire which is surrounded by a Cu O coating, thelead-through conductor being manufactured in known manner from acopper-clad wire of which part of the copper has been oxidised duringheating by an electrical process.

2 A discharge tube as claimed in claim 1, wherein the tube is a glowdischarge lamp.

3. A discharge tube as claimed in claim 2, characterized in that theconnection between the electrode and the lead-through conductor is awelded joint established by electrical process.

1. A DISCHARGE TUBE HAVING A WALL OF GLASS, WHICH TUBE CONTAINS AT LEASTMERCURY AND IS FURTHERMORE PROVIDED WITH AN INTERNAL ELECTRODE WHICH ISCONNECTED TO AN ELECTRICAL LEADTHROUGH CONDUCTOR CONSISTING MAINLY OFCOPPER-CLAD WIRE, AND IN WHICH AT LEAST THE PART OF SAID ELECTRICALLEAD-THROUGH CONDUCTOR LOCATED BETWEEN THE ELECTRODE AND THE GLASS WALLIS PROVIDED WITH AN OXIDE COATING, SAID COATING BEING IN DIRECT CONTACTWITH THE DISCHARGE SPACE OF THE DISCHARGE TUBE, WHEREIN SAID PART OF THELEAD-THROUGH CONDUCTOR CONSISTS OF A COPPER-CLAD WIRE WHICH ISSURROUNDED BY A CU20 COATING, THE LEAD-THROUGH CONDUCTOR BEINGMANUFACTURED IN KNOWN MANNER FROM A COPPER-CLAD WIRE OF WHICH PART OFTHE COPPER HAS BEEN OXIDIZED DURING HEATING BY AN ELECTRICAL PROCESS. 2.A discharge tube as claimed in claim 1, wherein the tube is a glowdischarge lamp.
 3. A discharge tube as claimed in claim 2, characterizedin that the connection between the electrode and the lead-throughconductor is a welded joint established by electrical process.